Design and performance evaluation of thermoelectric radiant cooling and heating panel

Abstract

기존의 천장 복사냉방 패널은 수배관이 부착된 패널을 천장에 설치하여 복사와 대류 열전달을 통해 실내 재실자의 온열환경을 제어함으로써, 공기 대류식 냉방 시스템에 비해 더 쾌적한 온열감을 유지할 수 있다. 하지만 냉매를 사용하는 증기압축식 사이클 기반의 냉동기를 통해 냉수를 획득하여 친환경 건축물의 설비 시스템으로는 부적합하며, 수배관의 사용으로 인해 시스템의 복잡도가 증가하여 시공이 어렵고 초기 설치비가 증가하는 문제점을 지니고 있다. 이에 본 연구에서는 비냉매 기반의 고체식 히트펌프인 열전모듈을 이용한 복사 냉난방 패널을 제안하였다. 열전모듈은 Peltier 효과를 기반으로 히트펌프로 동작하는 소자로 크기가 작고, 소음/진동이 없으며, 반응속도가 빠르고, 제어가 용이하다는 장점이 있어 패널의 온도를 간단하게 제어하는데 적합하다고 사료되었으며, 전류의 방향을 전환하면 열 이동의 방향이 제어가 가능하므로 냉방과 난방 두가지 용도로 동시에 활용하는 것 또한 용이하다. 열전 복사 냉난방 패널은 시스템의 간편성을 위해 공랭식으로 계획되었으며, 공조 공간 천장부 플래넘을 덕트로 활용하는 방안이 제안 되어 건식 복사 냉난방 패널로 제안 되었다. 이를 바탕으로 열전 복사 냉난방 패널의 성능 최적화를 위해 유한차분법 기반의 수치해석 모델이 정립되었으며, 설계 프로그램이 개발되었다. 개발된 설계 프로그램의 유효성 검증을 위해 열전 복사 냉난방 패널의 프로토 타입이 제작되었으며, 검증된 설계 프로그램을 이용하여 열전모듈의 최적 배치는 정삼각형 배치이며, 0.28 m의 간격으로 설치되었을 때 설계 기준을 만족함을 제시하였다. 본 열전 복사 패널의 냉난방 성능 및 에너지 해석을 목적으로 실험계획법을 이용한 성능 예측 모델 개발이 진행되었다. 냉방 성능 예측 모델은 에너지 소비량과 냉방량에 대해 실험을 진행하였으며, 개발된 모델은 추가 운전 데이터를 통해 실측값을 기반으로 검증되었다. 또한, 개발된 예측모델을 이용하여 연간 건물 에너지 시뮬레이션에 적용하는 프로세스와 설계 시 엔지니어들이 직관적으로 열전 복사 냉난방 패널의 냉방량을 파악할 수 있도록 성능 표를 도출하였다. 열전 복사 냉난방 패널의 난방 운전은 적합한 운전 방법 결정을 목적으로 수치해석 모델을 정립하였으며, 실험과 수치해석 시뮬레이션을 통해 열전 복사 패널의 난방은 Joule 효과를 기반으로 운전되는 것이 적합함을 검증하였다. 난방 성능 예측 모델은 마찬가지로 실험계획법 기반으로 개발되었으며, 에너지 소비량과 난방량에 대한 두 가지 모델이 도출되었다. 이를 바탕으로 개발된 열전 복사 냉난방 패널 성능 예측 모델을 이용하여 열전 복사 냉난방 패널과 외기 전담 시스템(Dedicated outdoor air system, DOAS)가 같이 적용되었을 때에 기존의 수배관식 천장 복사 냉방 패널 대비 연간 에너지 소비량을 시뮬레이션을 통해 비교하였다. 또한, 열전 복사 냉난방 패널의 운전 에너지 절감을 위해 직접식 증발 냉각을 공랭부에 설치하였을 때 효과에 대해 추가 분석한 결과, 기존 시스템에 비해 연간 16.1%의 에너지 절감이 가능함을 도출하였다. |The functions of the conventional hydraulic ceiling radiant cooling panel (CRCP) are based on convection and radiation to control a room condition. Therefore it sup-plies better thermal comfort than the convection air conditioner. However, the CRCP uses cold water from a chiller using refrigerant that has global warming po-tential and ozone deployment potential. Moreover, the CRCP system has difficulty of installing due to plumbing systems. In this study, the thermoelectric radiant cooling and heating panel (TERP) was suggested using the thermoelectric module (TEM), which is a solid-state heat pump without a refrigerant. It is based on the Peltier effect and has many advantages like compact size, easy controllability, and rapid response without- moving parts, noise, and vibration. The TEM can function as both cooling and heating by converting the direction of the input current. The TERP was designed as an air-cooled type for simple installation and the plenum space over the ceiling was to be used as a duct. In chapter 2, the development of the numerical analysis model using the finite dif-ference method (FDM) based on the basic design of TERP (i.e., air-cooler type) and construction to verify the developed simulation model is described. Simulation and experiment revealed that the triangular arrangement of TEM with a 0.28 m interval could satisfy the design standard for uniform temperature distribution of the radiant cooling and heating panel. In chapter 3, the development of empirical models to predict the cooling perfor-mance of the TERP, based on the experimental design method is explained. During the cooling operation, the independent variables were the room temperature, com-bined heat transfer coefficient at the surface of TERP, inlet air temperature, and face velocity of air in the duct. The developed models showed an R2 value over 0.99 and were validated in various operation conditions. Implementation examples are in-cluded as guidelines to use the developed models for energy simulation. In chapter 4, the evaluation of a suitable heating operation of the TERP using numerical analysis and experiments is detailed. The results revealed that the heating operation of the TERP showed better performance when it works based on the Joule effect, without operating a fan at the duct side. Empirical models were devel-oped to analyze the heating operation of the TERP. The independent variables were the room temperature, the target surface temperature of the TERP, and the combined heat transfer coefficient at the surface of the TERP. The developed models showed good agreement with the actual values with R2 over 0.94 and were validated by ex-periments. In chapter 5, the conducted annual energy simulations when the TERPs were used with the dedicated outdoor air system (DOAS) using the empirical models de-scribed in chapter 3 and 4 are given. The reference case was the DOAS with the CRCP. Two cases using the TERP, where one used only the TERP (Case 1) and the other used the direct evaporative cooler (DEC) assisted TERP (Case 2). The simula-tion results indicated that the TERP itself could not save energy due to a low coeffi-cient of performance (COP) of thermoelectric materials in the current stage. How-ever, the DEC assisted TERP with the DOAS system had better energy benefits by reducing 16.1% of annual operation energy compared to the DOAS with the CRCP.; The functions of the conventional hydraulic ceiling radiant cooling panel (CRCP) are based on convection and radiation to control a room condition. Therefore it sup-plies better thermal comfort than the convection air conditioner. However, the CRCP uses cold water from a chiller using refrigerant that has global warming po-tential and ozone deployment potential. Moreover, the CRCP system has difficulty of installing due to plumbing systems. In this study, the thermoelectric radiant cooling and heating panel (TERP) was suggested using the thermoelectric module (TEM), which is a solid-state heat pump without a refrigerant. It is based on the Peltier effect and has many advantages like compact size, easy controllability, and rapid response without- moving parts, noise, and vibration. The TEM can function as both cooling and heating by converting the direction of the input current. The TERP was designed as an air-cooled type for simple installation and the plenum space over the ceiling was to be used as a duct. In chapter 2, the development of the numerical analysis model using the finite dif-ference method (FDM) based on the basic design of TERP (i.e., air-cooler type) and construction to verify the developed simulation model is described. Simulation and experiment revealed that the triangular arrangement of TEM with a 0.28 m interval could satisfy the design standard for uniform temperature distribution of the radiant cooling and heating panel. In chapter 3, the development of empirical models to predict the cooling perfor-mance of the TERP, based on the experimental design method is explained. During the cooling operation, the independent variables were the room temperature, com-bined heat transfer coefficient at the surface of TERP, inlet air temperature, and face velocity of air in the duct. The developed models showed an R2 value over 0.99 and were validated in various operation conditions. Implementation examples are in-cluded as guidelines to use the developed models for energy simulation. In chapter 4, the evaluation of a suitable heating operation of the TERP using numerical analysis and experiments is detailed. The results revealed that the heating operation of the TERP showed better performance when it works based on the Joule effect, without operating a fan at the duct side. Empirical models were devel-oped to analyze the heating operation of the TERP. The independent variables were the room temperature, the target surface temperature of the TERP, and the combined heat transfer coefficient at the surface of the TERP. The developed models showed good agreement with the actual values with R2 over 0.94 and were validated by ex-periments. In chapter 5, the conducted annual energy simulations when the TERPs were used with the dedicated outdoor air system (DOAS) using the empirical models de-scribed in chapter 3 and 4 are given. The reference case was the DOAS with the CRCP. Two cases using the TERP, where one used only the TERP (Case 1) and the other used the direct evaporative cooler (DEC) assisted TERP (Case 2). The simula-tion results indicated that the TERP itself could not save energy due to a low coeffi-cient of performance (COP) of thermoelectric materials in the current stage. How-ever, the DEC assisted TERP with the DOAS system had better energy benefits by reducing 16.1% of annual operation energy compared to the DOAS with the CRCP.